There is no current technology for routine measurement of shunt flow (Qp:Qs - ratio of pulmonary to systemic blood flow) in newborns and small children in the intensive care unit (ICU). Current methods either require placement of highly invasive catheter or depend on assumptions, leading to risky and less accurate measurement of shunt flow. Timely and accurate quantitative assessment of Qp/Qs permits successful pharmacologic, ventilator or fluid therapy or in time surgical intervention. Hence routine measurement of shunt flow is vital in the management of critically ill newborn and small children with cardiac defects. This SBIR grant will allow us to develop mathematical models and algorithms accounting for various shunts, clinical and physiological conditions. These will then be implemented into a monitor that could be used clinically at the bedside in a non-invasive manner with patients having in situ arterial and central venous catheters. The approach is based on well-established indicator dilution principles using innocuous isotonic saline as an indicator. These factors make the proposed monitor eminently suitable for used with neonatal and pediatric ICU patients. Main objectives of this proposal include - 1) Development of mathematical models and software algorithms for accurately quantifying shunt flow 2) Perform feasibility and validation testing of shunt flow measurements in animal models 3) Perform feasibility and clinical comparison of shunt flow measurements in newborns and small children. These objectives will be achieved in a concerted effort by Transonic's R&D staff, and its collaborators at University of Pittsburgh, PA and Crouse Hospital, NY. Successfully accomplishing Phase-I goals will test the feasibility of the proposed approach and guide further research to develop and clinically validate the first of its kind Bedside monitor for quantitative measurement of shunt flow in critically ill newborns and small children.